When packers are set to isolate zones in a subterranean location the differential pressure across the sealing element can force that element to extrude axially in the direction of the pressure differential. Backup ring structures have been used to address the tendency to extrude under differential pressure loading. A collection of segments that overlap and can be forced out by relative axial component movement have been tried such as in US Publication 2011/0036561 and US Publication 2010/0071908. Despite the use of many segments to make an annular backup assembly the nature of the way the parts fit together and move radially does not always allow the components to adequately conform to out of roundness or surface irregularities of the surrounding tubular or the wellbore wall.
Some designs provided cup shaped backup ring stacks that has staggered slots as between layers as an extrusion barrier in expansion ranges up to 25%. U.S. Pat. No. 6,827,150 is an illustration of one such design. Others are U.S. Pat. No. 7,128,145; US Publication 2004/0149429 and 2005/0115720. Other high expansion packer designs are US Re 32,831; U.S. Pat. Nos. 6,311,778; 6,318,461 and 6,164,375.
Despite the variation of designs for backup rings as extrusion barriers the issue of gaps around the periphery remained and is addressed by the present invention.
In the field of metal to metal seals a design has been developed that features a bow shaped sealing element that is axially compressed at opposed base locations and then pinched between two relatively movable members as the element extends to make metal to metal contact with the opposing tubular as illustrated in US Publication 2009/0071641. In one embodiment soft metals or elastomers can be added at the opposing wall contact location to address the wall imperfections of the surrounding tubular to enhance the performance of the seal. A variation of this design for seals uses a flimsy metal annular shape filled with rubber and compressed on opposed ends so that the metal outer shape obtains structure from the interior fill material to seal against the surrounding tubular. This design is shown in U.S. Pat. No. 5,775,429 with many variations including an application as an extrusion barrier in FIGS. 8 and 9.
The present invention focuses on improving performance of backup rings where conformance to irregular surfaces is a feature. Axial relative movement results in collapsing a bow shaped backup ring on either side of a sealing element when the backup rings are converted to a teardrop shape by pinching along a length of the radially extending shape with relative axial movement between compressing members that support the ends of the bow shape. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.